1. Field of the Invention
The present invention relates to a microvalve and a microchip having a micro fluidic structure, and more particularly, to a bi-stable and phase change type microvalve provided in a micro fluidic structure and a microchip including the microvalve.
2. Description of the Related Art
In general, a valve refers to an apparatus that is connected to a pipe to control the amount of flow or pressure of a fluid. A microvalve and other apparatuses comprising a microvalve related to a micro fluidic structure have received wide attention, particularly in a bio-chemical field including a micro total analysis system (μTAS). The microvalve is widely used not only in the μTAS related to the development of new medicines, a clinical diagnosis system, and a biomedical research field such as a DNA, but also in an inkjet print field.
The microvalve developed with the development of a micro-electromechanical system (MEMS), or a so-called MEMS valve, has a important role in the micro fluidic structure with a micropump, as an important device having functions of allowing, limiting, and blocking the flow of a fluid including gas or liquid. The microvalves manufactured using a fine processing technology have a variety of structures and sizes from several micrometers to about 1 mm according to the type of driving and purpose.
A phase change valve has been studied among the various types of microvalves. The phase change valve refers to a tangible valve that is included in the micro fluidic structure to exist in a solid state and controls the flow of a fluid in a mode. The state of the phase change valve is changed from the solid state to a liquid state, causing a displacement or deformation, when the mode is changed to another mode. U.S. Pat. No. 6,679,279 and U.S. Patent Publication No. 2004-0219732 disclose the above phase change valve. A conventional phase change valve is described below with reference to FIGS. 1A, 1B, 2A, and 2B.
FIGS. 1A and 1B show an example of the conventional phase change valve, in which FIG. 1A shows a closed mode in which a channel is closed and FIG. 1B shows an open mode in which the channel is open. Referring to FIGS. 1A and 1B, a microchannel 21 is formed in a substrate 20. A well 22 is formed at a side of the channel 21. A solid wax plug 40 is provided in the microchannel 21 at the upper stream thereof with respect to the well 22. A solid wax is a material which exists in a solid state at the room temperature and its fluidity grows as it is heated. A typical material for the solid wax is paraffin wax.
A heating portion 30 capable of selectively radiating heat is provided around the solid wax plug 40. When the heating portion 30 radiates heat in the state as shown in FIG. 1A, the solid wax plug 40 is melt. A melt wax 40′ flows into the well 22 by the pressure of a fluid flowing in the microchannel 21 and becomes solid in the well 22. However, since the mode change of the conventional phase change valve 101 is irreversible, once the valve opens, the valve cannot be reused.
FIGS. 2A and 2B show another example of the conventional phase change valve. Referring to FIGS. 2A and 2B, a phase change valve 102 has a Y shaped connection portion where an inlet portion 23, an outlet portion 24, and a vent portion 25 meet. A heating portion 30 is provided a portion extending from the Y shaped connection portion to the vent portion 25. As shown in FIG. 2A, when the valve 102 is in an open mode, a solid wax plug 42 is located in the Y shaped connection portion. When the valve 102 is in a closed mode as shown in FIG. 2B, the solid wax plug 42 is moved to the vent portion 25.
For mode change, the solid wax plug 42 is melt using the heating portion 30 and a melted wax is moved by an air pressure and vacuum chamber (or pump) that is selectively connected to a side of the vent portion 25. Thus, this type of the valve 102 needs a connection to a high pressure or vacuum chamber (or pump) using another valve for the driving of the valve. To facilitate miniaturization of the valves in units of micrometers and provide a micro fluidic structure which can be reused, the above disadvantages that the conventional phase change valves 101 and 102 have must be overcome.